In contrast to the changes resulting only from the often counteracting forces of mutation, selection, drift, and intraspecific gene flow, evolution in natural hybrid systems is usually dramatic. One genetic consequence of hybridization is interspecific gene flow. This process may have profound evolutionary consequences if it leads to increased fitness, expansion of geographic ranges, and speciation. The horizontal transfer of genes via hybridization may act as a natural form of genetic engineering. I have provided evidence that one of the most widely distributed and successful waterflea species (Daphnia) has received genes via hybridization and backcrossing with related species. Further work will characterize this interspecific gene flow in detail and test hypotheses concerning the evolutionary and ecological significance of these alien genes.

Our planet is a biotic kaleidoscope and each turn of the human hand yields a fascinating yet unpredictable new mosaic. The rapidity and complexity of recent global change has both excited and bewildered evolutionary biologists, who once lamented that their discipline might be studied in a handful of exemplary systems. Studies of the genetic consequences of biological invasions often provide insights into problems in evolution, ecology, and conservation biology. For example, invasions can lead to rapid evolution from severe founder effects and novel selection regimes or even to quantum evolutionary events such as the creation of hybrid species, new genetic variants and polyploid derivatives. Using genetic markers, I established that the most important component of zooplankton biomass in Lake Erie, the waterflea Daphnia galeata, is now dominated be a hybrid swarm created by the introduction of Eurasian plankton (probably from ships' ballast water). I also showed that alien hybrid swarms have spread to nearby lakes and rapidly eroded gene combinations of native populations and apparently replaced native taxa. It is now clear that, not only are cryptic invasions occurring, but also that they can precipitate genetic revolutions in the native taxa. Ongoing and future studies will investigate in detail the genetic architecture of Eurasianized Daphnia in Lake Erie and nearby lakes. We aim to gain a better understanding of the processes that affect the success and spread of the Eurasianized Daphnia by testing ecological and genetical hypotheses.

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